Numerous communications and navigation systems are multi-band, covering two or more different frequency bands for different applications or compatibility with different systems around the globe. For example, a system may be configured to cover the UHF (ultra high frequency; approximately 300-3000 MHz) band, GPS (global positioning system) frequencies, and satellite communication frequency bands, such as those used by the Iridium™, SATCOM™ and GPS systems. A majority of systems would use multiple antennas to cover the UHF/GPS/Iridium™ bands.
Modern day technology and fabrication methods have allowed electronic components such as radio frequency (RF) receivers and processing electronics to be packaged in extremely small housings. The RF antenna becomes the limiting factor in the size of many devices. As the size of the antenna is reduced below a quarter wavelength, either the gain or bandwidth suffers. As a result, to maintain a moderate gain level, a system may have to contend with very narrow bandwidths for the antenna. Narrow bandwidth leaves the antenna susceptible to being pulled off frequency when placed near external objects. In addition, for multi-band systems that use multiple frequencies, such as a communication link at UHF and as well positioning information (GPS), two separate antennas are needed, one for each frequency band, due to restrictions on the antenna bandwidth.